The Queen arriving at King's Lynn train station last December without Philip. [Photo: PA]

But royal producer Nick Bullen told ‘The Royal Box’ on a previous episode that he thinks the Queen will never step down as monarch because abdication is now seen as ‘a dirty word in the royal household’.

Elizabeth’s uncle Edward VIII caused upheaval for the firm when he abdicated the throne in December 1936, less than a year into his reign. He sparked a constitutional crisis when he proposed to American divorcee Wallis Simpson.

After Edward stood down, the Queen’s father, King George VI, became king despite having never anticipated that he would be monarch and making the then Princess Elizabeth heir to the throne at the age of 10.